Note: Descriptions are shown in the official language in which they were submitted.
CA 02354311 2001-07-30
FUEL INJECTION SYSTEM FOR A TWO-STROKE ENGINE
Field of the Invention
[0001] The present invention relates to a fuel injection system for a two-
stroke engine. In
particular, the present invention concerns a fuel inj ection system for a two-
stroke engine with
crankcase scavenging, with at least one transfer duct. The transfer port to
the transfer duct,
which opens into the cylinder, is controlled by the engine piston. A fuel
injector is positioned
in the transfer duct, the injection jet from the injector being directed onto
the side of the piston
crown that is proximate to the combustion chamber, the axis of the injection
jet subtending an
angle of less than 90° with the axis of the piston. The injection jet
is directed, for the most
part at least, onto that half of the piston crown that is opposite the exhaust
port.
Background of the Invention
[0002] European Patent No. 302 045 B2 describes a two-stroke engine in which
the injector is
configured as a mufti-orifice injector, and in which the injection process for
the range of
higher engine speeds begins before the transfer port of the transfer duct is
uncovered by the
piston, so that some of the fuel can be pre-vaporized in the transfer duct.
This is necessary, in
particular, if the amount of time required for injection exceeds the amount of
time for which
the transfer ducts are open, as may be the case at very high engine speeds. In
such a case,
however, one disadvantage is that essentially injection takes place radially
to the cylinder
wall, and in the direction of the scavenging gas flowing into the cylinder by
way of the trans-
fer ducts. When this happens, it is scarcely possible to avoid unburned fuel
flowing out of the
combustion chamber into the exhaust, and this in its turn results in a loss of
fuel and increased
hydrocarbon emissions.
CA 02354311 2001-07-30
[0003] In order to prevent or reduce the fuel-air mixture from flowing through
the combustion
chamber into the exhaust to the maximum possible extent, in a modified version
of the two-
stroke engine described heretofore, European Patent No. 302 045 B2 proposes
that the piston
be configured as a deflector-crown piston that has a rounded, concave
deflector surface on the
same side as the transfer port. The jet from the injector is directed, at
least in part, onto said
deflector surface. (See also Austrian Patent No. 3 394 U1).
[0004] U.S. Patent 4,779,581 describes another two-stroke engine, in which
fuel is injected in
the same direction as the scavenging gas that is flowing into the cylinder. In
this engine, the
fuel is injected in the direction of the spark plug, away from the top surface
of the piston.
[0005] It is also known that low-pressure injectors can be used. Low pressure
injectors intro-
duce the fuel directly into the combustion chamber when the piston has
uncovered the exhaust
duct or transfer ducts. (See, e.g., U.S. Patent No. 5,762,040, German Patent
No. 39 13 629
C2, and German Patent No. 37 44 609 A1.) However, according to these
publications, be-
cause the fuel is injected not into the transfer duct but rather directly into
the cylinder through
a separate port, injection can only take place once the piston has uncovered
the injection port.
Otherwise, the fuel mixture would be injected directly onto the piston skirt,
which, on the one
hand, would result in inadequate preparation of the mixture and, on the other,
would result in
the film of lubricating oil being washed off the piston and this, in turn,
would increase the
danger of damage being done to the engine.
[0006] The same difficulty arises with European Patent No. 302 045 B2 and
Austrian Patent
No. 3 394 U1. In both engine designs, the injector nozzles open out into the
transfer ducts.
Although the injectors are almost perpendicular to the piston skirt, namely,
the side of the
piston skirt that is most greatly stressed (the cyclic pressure and back-
pressure side), in the
case of advanced injection of fuel before the edge of the transfer port is
uncovered by the
CA 02354311 2001-07-30
piston, the film of lubricating oil is washed off the piston, thereby
curtailing the service life of
the engine.
[0007] In addition, German Patent No. 37 44 609 describes the use of at least
two injectors,
each injector having its own, dedicated fuel-supply. In this engine, it is
possible to activate
each injector separately as a function of the operating parameters of the
engine.
[0008] According to U.S. Patent 5,762,040 A, two direct-injection low-pressure
injectors can
be provided for each cylinder. These injectors inject fuel directly into the
cylinder and are
connected to a common fuel-supply system. As before, the injectors are
directed essentially
towards the exhaust duct, so that a not insignificant loss of fuel, and the
concomitant escape of
unburned gasoline, have to be taken into account.
[0009] As indicated, in each of the prior art two-stroke engine designs, the
fuel injection
systems do not provide reduced emissions across a wide range of engine
operating speeds.
[0010] In addition, the prior art engines also experience a decrease in
performance across a
range of operating parameters in addition to experiencing an increase in
unwanted exhaust
emissions.
Summary of the Invention
[0011] Therefore, it is an object of the present invention to provide a fuel
injection system for
a two-stroke engine that maintains or increases performance of the engine
across a range of
operating parameters while also reducing exhaust emissions from the engine by
solving the
problems of the prior art listed above.
[0012] Accordingly, one aspect of the present invention is the provision of at
least two fuel
injectors, disposed so as to be essentially parallel to each other and so as
to subtend an angle
of 20° to 50°, preferably 35°, with the axis of the
cylinder, the injector being directed towards
CA 02354311 2001-07-30
the side of the piston crown that is proximate to the combustion chamber. The
fuel injectors
open out into the side transfer ducts, preferably one injector into one side
transfer duct on the
left-hand side and one on the right-hand side, adjacent to a rear boost port.
The arrangement
of the fuel injectors in the side transfer ducts means that the fuel that is
added to the gas (air or
a combination of air, vaporized fuel, and/or oil (among other components)) is
always injected
almost perpendicularly (i.e., across and partly against) to the gas flowing
into the combustion
chamber. This results in the greatest possible flow differential between the
inflowing gas and
the fuel that is injected, and results in superior, favourable mixing
conditions. Arrangement
of the fuel injectors in this manner also permits the complete (or nearly
complete) vaporiza-
tion of the fuel and also prevents unburned hydrocarbons from being exhausted
from the
cylinder, since no unvaporized fuel can be sprayed into the exhaust.
[0013] According to the present invention, it is preferred that the injectors
be configured as
multi-orifice injectors, since these generally provide for finer vaporization
as compared to
single-orifice nozzles, given identical injection parameters (i.e., pressure,
flow, etc.).
[0014] During development of the present invention, the inventors realized
that, primarily in
the range of greater engine speeds and loads when the amount of time available
for injecting
the fuel is very small, the fuel can be injected before the transfer port to
the side transfer duct
is uncovered. This means that some of the fuel can be pre-vaporized in the
transfer duct. This
ensures that sufficient fuel can be introduced into the cylinder, even at high
engine speeds.
[0015] To be able to match the quantity of fuel that is introduced into the
cylinder to particu-
lar demands, such as load and engine speed, the injectors may be activated
independently of
each other. Thus, in the partial-load range, only one of the two injectors may
be active and, in
contrast to this, when the engine is under full load, both the injectors may
supply fuel to the
cylinder. With such an arrangement, it also may be possible to have the
injectors work in
CA 02354311 2001-07-30
alternation when the engine is operating under partial load, so as to avoid
localized overheat-
ing of the engine. To this end, one injector is activated for one cycle, and
the other injector is
activated for the subsequent cycle.
[0016] Another way of matching the quantity of fuel injected to the load on
the engine is to
use two injection valves of different sizes, which is to say, valves with
different flow charac-
teristics. The smaller of the two is designed to deliver fuel mainly when the
engine is idling
or running under partial load. The other is activated only when the engine is
operating under
a specific load or at a specific speed, so that the demand for fuel can be
satisfied, especially
when the engine is operating under full load.
Brief Description of the Drawings
[0017] An example of the objects of the present invention is shown in the
drawings appended
hereto, like reference numbers indicating like parts throughout. In the
drawings:
[0018] Figure 1 is a partial cross-section of one embodiment of an injection
system according
to the present invention, as viewed from above;
[0019] Figure 2 illustrates the injection system in cross-section, taken on
the line II-II shown
in Figure 1;
[0020] Figure 3 shows the injection system in cross-section, taken on the line
III-III shown in
Figure 1; and
[0021] Figure 4 depicts the injection system shown in Figure 1, together with
crankcase, in
partial cross-section, as viewed from the side.
Detailed Description of the Preferred Embodiments
CA 02354311 2001-07-30
[0022] As shown in the accompanying figures and as is conventionally known, a
two-stroke
engine includes a cylinder 1 having an exhaust port 2, side transfer ports 3,
and a rear boost
port 4. The cylinder 1 is mounted to a crankcase 9 and a cylinder head 8 is
mounted to the
cylinder 1 to close the cylinder 1. A reed valve 5 is mounted in the intake
path of the cylinder
1 and allows air to pass from the atmosphere to the crankcase 9. In other
known embodiments,
the reed valves can be mounted in the crankcase 9 itself.
[0023) In a conventional carbureted two-stroke engine, an air and fuel mixture
is sucked into
the crankcase 9 through the reed valve 5 as a piston 10 moves upward in the
cylinder 1.
When the piston 10 reaches the top of its stroke and begins moving downward in
the cylinder,
it compresses the air and fuel charge in the crankcase 9, thereby closing the
reed valve 5. (See
Figure 4.) When the piston has moved downward in the cylinder sufficiently to
open the
transfer ports 3a, 3b and rear boost port 4, the compressed air and fuel
charge is pushed up-
ward through these ports into the cylinder 1. (See~e.Q., Figs. 1 and 3.) This
charge also
serves to push the spent exhaust gases from the previous combustion out of the
cylinder
through the exhaust port 2. However, considering all of the operating
parameters of the
engine, it is difficult to do this without either having incomplete scavenging
of the exhaust
gases from the cylinder or pushing some of the air and fuel charge into the
exhaust port. Both
occurrences affect the performance of the engine but the latter also increases
hydrocarbon
emissions from the engine since unburned fuel is being exhausted into the
atmosphere.
[0024] In the present invention, two fuel injectors 6 are mounted beside the
rear boost port 4.
They are also mounted to have a downward angle of injection into the cylinder,
with the angle
preferably being approximately 35° from a plane normal to an axis of
the cylinder. As would
be appreciated by those skilled in the art, however, the angle can be varied,
as appropriate, to
achieve desired operating conditions of the engine. It has been shown,
however, that the
CA 02354311 2001-07-30
angle preferably should be within the range of 20° to 50° in
order to achieve satisfactory
results with respect to engine performance and emissions. Figure 2 illustrates
the range of the
complementary angles between 40° and 70°. The fuel is not
injected radially, towards the
center of the cylinder, as in the prior art. Instead, it is injected
tangentially to the cylinder 1.
As shown, the fuel is injected in a direction substantially parallel to a
plane bisecting the
cylinder 1 through its center point.
[0025] It is preferred that the two injectors 6 be disposed so as to be
parallel to each other. So
arranged, the two injectors 6 can be supplied with fuel very simply by way of
a common fuel
rail 7; this is particularly so when a number of cylinders are disposed in a
row. Each injector
6 opens out into one of the side transfer ducts 3a that are located alongside
the rear boost port
4. The injectors 6 thus inject the fuel almost perpendicularly (i.e., across
and partly against)
to the gas 13 that is flowing into the cylinder through the side transfer
ducts 3a (the flow
patterns of the gas that enters the cylinder through the various ports are
indicated by the
arrows shown in the drawings). This results in the best possible vaporization
of the fuel 12
and the best possible mixing with the gas 13 that enters the cylinder by way
of the transfer
ducts. Furthermore, injection takes place at the upper edge 14 of the side
transfer ports 3a,
where the flow velocity is greatest when the gas 13 flows into the cylinder 1,
so that the fuel
and air are mixed even more thoroughly. The gas 13 flowing into the cylinder 1
transversely
to the injection jet 12 also acts as a barrier, because it prevents the fuel
that is injected from
flowing across the cylinder 1 into the exhaust port 2.
[0026] The flow of gas 13 that emerges from the rear boost port 4 and which is
directed
upward (see Figure 3) does not interact directly with the injected fuel 12.
However, because
the flow of gas 13 causes the flows of gas emerging from the transfer ports
3a, 3b to flow
CA 02354311 2001-07-30
upward (i.e., it deflects them towards the cylinder head), it ensures that the
injected fuel 12 is
also deflected in this direction, so that all of the fuel is burned.
[0027] In addition, injection takes place in the direction of the maximum
width W of the side
transfer ducts 3a, 3b and not across the low height of the transfer port 3a.
Accordingly, injec-
tions taken place from the upper edge 14 of the transfer port towards the
lower edge of the
transfer port, as was usually the case in the prior art.
[0028] Even though the major portion of the fuel 12 that is injected is
directed onto the half of
the piston that is remote from the exhaust port 2, some of the injected fuel
can nevertheless
interact with the gas emerging from the transfer ducts 3b that are more remote
from the point
of injection. This is further facilitated in that the flow of gas from the
side transfer ducts 3b is
not oriented radially inward, but rather in the direction toward the rear
boost port 4, so that at
least a considerable component of the gas flow is directed against the
injection jet 12. In this
way, mixing is improved to an even greater extent, and it is ensured that the
fuel 12 that is
injected cannot enter the exhaust port 2.
[0029] Because of the fact that the injectors 6 are inclined slightly towards
the side of the
piston 10 that is proximate to the combustion chamber, a certain amount of
fuel 12 can reach
the crown of the piston, vaporize on this, and thus cool the piston as a
result of the heat loss
caused by this vaporization.
[0030] As indicated above, it is preferred that fuel be supplied to the fuel
injectors 6 through a
common fuel rail 7. However, as would be appreciated by those skilled in the
art, the fuel
injectors 6 may be supplied with fuel from separate fuel lines.
[0031] Under partial load conditions, the timing of the injection of the fuel
from the fuel
injectors into the cylinder will preferably be delayed until later in the
scavenging phase (but
prior to closing of the scavenging ports 3a, 3b and 4 by the piston 10). This
delay in injecting
CA 02354311 2001-07-30
fuel into the cylinder reduces or eliminates unburned fuel from escaping out
of the exhaust
port to the atmosphere during operation of the engine. The operating
conditions of the engine,
such as throttle opening, engine speed ("rpm"), etc., will dictate the amount
of fuel injected by
the injectors during each injection cycle.
[0032] The amount of fuel injected during each injection cycle is generally
controlled by the
length of the injection cycle. Therefore, at operating conditions requiring
higher amounts of
fuel, e.g. under full load condition, the duration of the injection cycle will
be longer. This may
require that the injection cycle starts sooner (as compared with lower fuel
requiring condi-
lions) to provide sufficient time for the injection cycle prior to closing of
the scavenging ports.
When the engine is running under full load, injection can take place before
the piston 10
begins to uncover the transfer ducts. (See Figure 4.) In this case, a large
part of the fuel 12
that is injected strikes the hot piston skirt, where it is prevaporized and is
carried into the
cylinder 1 by the flow of gas, once the transfer duct 3a has been uncovered.
[0033] This earlier injection of the fuel into the cylinder 1 is still less
likely to result in un-
burned fuel escaping out of the exhaust port as compared with a carbureted
engine, since the
expansion chamber will generally be tuned for such operating conditions to
prevent the escape
of unburned fuel into the atmosphere.
[0034] The use of multiple fuel injectors increases the fuel delivery capacity
of the injection
system and provides for shorter injection cycles. This is especially important
at high rpm and
full throttle (i.e., throttle opened to a great extent) conditions where the
time available for
injection is smaller (due to the high rpm) but the amount of fuel required is
larger. Alterna-
tively, three or more fuel injectors can be used per cylinder in more
demanding applications,
as can one fuel injector per cylinder in less demanding applications.
Furthermore, the use of
multiple fuel injectors can be staged such that one fuel injector operates at
less demanding
CA 02354311 2001-07-30
operating conditions and a second (or further) injector begins operation at
more demanding
conditions to supplement the fuel delivery by the first fuel injector.
Moreover the fuel injec-
tors do not necessarily need to be of the same size or type. Quite contrary to
this one fuel
injector could be designed to be smaller than the other one and be operated
only under idle
speed and under part load to provide better sensibility and reproducibility
under these operat-
ing conditions where small quantities of fuel are demanded.
[0035] In the preferred embodiment, the control of the fuel injectors is by an
Electronic Con-
trot Unit, ("ECU"). The ECU takes into account one or more operating
conditions, such as
throttle opening, rpm, engine temperature, atmospheric temperature, barometric
pressure, etc.,
determines the appropriate fuel delivery for such conditions, and controls the
fuel injectors to
deliver the desired amount of fuel.
[0036] The reduction of emissions due to the present fuel injection system can
be
complemented by the use of a catalytic converter in the exhaust system and
reductions of oil
supplied to the engine for lubrication, for instance, due to more precise
metering and spot
delivery.
[0037] The present invention was developed preferably to meet the operating
requirements of
a snowmobile. As would be appreciated by those skilled in the art, snowmobiles
operate at
high engine speeds and loads. As discussed, the fuel injection system of the
present invention
improves performance across a range of operating parameters, including high
speed (and/or
high load) operation. While designed with the requirement of a snowmobile in
mind,
however, the present invention could be applied to an engine designed for any
type of vehicle
including a personal watercraft, ATV, or the like.
[0038] The present invention is not meant to be limited solely to the
embodiments described.
To the contrary, the embodiments described may be modified in various ways
without
to
CA 02354311 2001-07-30
departing from the scope and content of the present invention. Modifications
that may be
apparent (or will become apparent) to those skilled in the art are also
intended to fall within
the scope of the present invention.
m
